Studies have been made of the species composition and variation of benthic marine algae at subtidal zone of Uljin on the east coast of Korea. Destructive method was employed to measure biomass over four seasons (2000-2002). Of 87 marine algae species identified, 11 were Chlorophyta, 29 were Phaeophyta and 47 were Rhodophyta. Dominant species in biomass were Ulva pertusa, Undaria pinnatifida and Sargassum piluliferum in summer, Laminaria religiosa, Sargassum fulvellum and Gigartina tenella in autumn, Codium fragile, Undaria pinnatifida, Sargassum horneri, S. piluliferum and S. ringgoldianum in winter, and Undaria pinnatifida, Dictyopteris divaricata, Sargassum confusum and S. horneri in spring. In general, green algae (Ulva pertusa, Codium fragile) and brown algae (Undaria pinnatifida, Sargassum fulvellum, S. horneri, S. piluliferum) appeared predominantly in the 3, 6 m depths and red algae (Gelidium amansii, Plocamium telfairiae) in the 9, 12 m depths. The barren ground of the rocky shore might provide the decrease of benthic marine algae biomass and species.